R scope: force variable substitution in function without local environment

Question

I\'m defining functions in a loop and trying to force evaluation of a loop variable without having to carry around a private environment.

Example: a set of functions

Answer 1

Unfortunately base R lacks a function for making functions by hand, but pryr supplies make_function:

library(pryr)

handlers <- list()
for (i in 1:6) {
  body <- substitute(message(i), list(i = i))
  f <- make_function(alist(), body)

  handlers[[paste0('h', i)]] <- f
}

Note the use of substitute to manually modify a quoted call.

Another cool (IMO!) function in pryr is unenclose, which unencloses a function by substituting in the variables defined in the enclosing environment:

msg <- function(i) {
    force(i)
    function () message(i)
}
msg(1)
# function () message(i)
# 
unenclose(msg(1))
# function () 
# message(1)

But their really is no downside to using the original closure.